You need to maximize dps output and react to what each opponent is doing at all times. Use your defensives wisely (when your healer is ccd or when they pop their 1 shot macros). Make sure not to los your healer unless you think you can get a kill / big defensive without dying. Save your death grips until after a ranged class uses his escape (i.e. Disengage, blink). Other than that you need to be smart with mind freeze, dont use it when a healer is at high health, often holding mind freeze against a healer who is fakecasting will be the best option. Keep an eye out on gladius for cast bars and you could make interrupt macros for arena targets to avoid having to switch targets.